Digital watermarking compressed video captured from aerial sensors

ABSTRACT

Digital watermarking technology is used in conjunction with compressed video captured from aerial, unmanned apparatus, such as satellites and aircraft. One implementation includes a method of capturing video depicting at least a portion of the earth&#39;s surface, the video captured by an aerial, unmanned apparatus; compressing the captured video; and hiding a first digital watermark in the compressed captured video through alterations to data representing the compressed video. The first digital watermark is generally imperceptible to a human observer of the video. And the digital watermark has a plural-bit payload including at least geographical metadata associated with the captured video. Other implementations are also provided.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.10/778,762, filed Feb. 13, 2004 (issuing as U.S. Pat. No. 7,099,492).The Ser. No. 10/778,762 application is a division of U.S. patentapplication Ser. No. 09/800,093, filed Mar. 5, 2001 (now U.S. Pat. No.7,061,510). The above U.S. patent documents are hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to image management and processing, and isparticularly illustrated in the context of near real-time management ofsatellite and other aerial imagery, and automatic revision of map databased on such imagery.

BACKGROUND AND SUMMARY OF THE INVENTION

Acquisition of aerial imagery traces its history back to the Wrightbrothers, and is now commonly performed from satellite and space shuttleplatforms in addition to aircraft.

While the earliest aerial imagery relied on conventional filmtechnology, a variety of electronic sensors are now more commonly used.Some collect image data corresponding to specific visible, UV or IRfrequency spectra (e.g., the MultiSpectral Scanner and Thematic Mapperused by the Landsat satellites). Others use wide band sensors. Stillothers use radar or laser systems (sometimes stereo) to sensetopological features in 3 dimensions.

The quality of the imagery has also constantly improved. Some satellitesystems are now capable of acquiring image and topological data having aresolution of less than a meter. Aircraft imagery, collected from loweraltitudes, provides still greater resolution.

For expository convenience, the present invention is particularlyillustrated in the context of a Digital Elevation Model (DEM). A DEM,essentially, is an “elevation map” of the earth (or part thereof). Onepopular DEM is maintained by the U.S. Geological Survey and detailsterrain elevations at regularly spaced intervals over most of the U.S.More sophisticated DEM databases are maintained for more demandingapplications, and can consider details such as the earth's pseudo pearshape, in addition to more localized features. Resolution ofsophisticated DEMs can get well below one meter cross-wise, and down tocentimeters or less in actual elevation. DEMs—with their elevationdata—are sometimes supplemented by albedo maps (sometimes termed texturemaps, or reflectance maps) that detail, e.g., a grey scale value foreach pixel in the image, conveying a photographic-like representation ofan area.

There is a large body of patent literature that illustrates DEM systemsand technology. For example:

U.S. Pat. No. 5,608,405 details a method of generating a DigitalElevation Model from the interference pattern resulting from twoco-registered synthetic aperture radar images.

U.S. Pat. No. 5,926,581 discloses a technique for generating a DigitalElevation Model from two images of ground terrain, by reference tocommon features in the two images, and registration mapping functionsthat relate the images to a ground plane reference system.

U.S. Pat. Nos. 5,974,423, 6,023,278 and 6,177,943 disclose techniques bywhich a Digital Elevation Model can be transformed into polygonalmodels, thereby reducing storage requirements, and facilitating displayin certain graphics display systems.

U.S. Pat. Nos. 5,995,681 and 5,550,937 detail methods for real-timeupdating of a Digital Elevation Model (or a reference image basedthereon), and are particularly suited for applications in which theterrain being mapped is not static but is subject, e.g., to movement ordestruction of mapped features. The disclosed arrangement iterativelycross-correlates new image data with the reference image, automaticallyadjusting the geometry model associated with the image sensor, therebyaccurately co-registering the new image relative to the reference image.Areas of discrepancy can be quickly identified, and the DEM/referenceimage can be updated accordingly.

U.S. Pat. No. 6,150,972 details how interferometric synthetic apertureradar data can be used to generate a Digital Elevation Model.

From systems such as the foregoing, and others, a huge quantity ofaerial imagery is constantly being collected. Management andcoordination of the resulting large data sets is a growing problem.

In accordance with one aspect of the present invention, digitalwatermarking technology is employed to help track such imagery, and canalso provide audit trail, serialization, anti-copying, and otherbenefits.

In accordance with another aspect of the invention, incoming imagery isautomatically geo-referenced and combined with previously-collected datasets so as to facilitate generation of up-to-date DEMs and maps.

The foregoing and additional features and advantages of the presentinvention will be more readily apparent from the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart of steganographically embedding auxiliary datain imagery.

FIG. 2 shows a flow chart of steganographically hiding information inmedia.

FIG. 3 shows a flow chart of steganographically hiding or embeddinginformation in an image or media, including an act of decoding firstinformation hidden or embedded in the media or image.

FIG. 4 shows a flow chart of steganographically hiding or embeddingsecond information in media or an image, including overlaying the firstinformation.

FIG. 5 shows a flow chart of steganographically hiding or embeddingsecond information in media or an image, including overwriting the firstinformation.

DETAILED DESCRIPTION

(For expository convenience, the following specification focuses onsatellite “imagery” to illustrate the principles of the invention. Theprinciples of the invention, however, are equally applicable to otherforms of aerial surveillance data and other topographic/mappinginformation. Accordingly, the term “image” should be used to encompassall such other data sets, and the term “pixel” should be construed toencompass component data from such other data sets.)

When new aerial imagery is received, it is generally necessary toidentify the precise piece of earth to which it corresponds. Thisoperation, termed “georeferencing” or “geocoding,” can be a convolutedart and science.

In many systems, the georeferencing begins with a master referencesystem (e.g., latitude and longitude) that takes into account theearth's known deformities from a sphere. Onto this reference system theposition of the depicted region is inferred, e.g., by consideration ofthe satellite's position and orientation (ephemeris data), opticalattributes of the satellite's imaging system, and models of thedispersion/refraction introduced by the earth's atmosphere.

In applications where precise accuracy is required, the foregoing,“ephemeris,” position determination is refined by comparing features inthe image with the placement of known features on the earth's surface(e.g., buildings and other man-placed objects, geological features,etc.) and compensating the georeference determination accordingly. Thus,for example, if the actual latitude and longitude of a building is known(e.g., by measurement from a ground survey—“ground truth”), and thecorresponding latitude and longitude of that building as indicated inthe georeferenced satellite imagery is different, the reference systemapplied to the satellite data can be altered to achieve a match.(Commonly, three or more such ground truth points are used so as toassure accurate correction.)

Ground-truthing is a tedious undertaking. While computer methods can beused to facilitate the process, the best ground truth correction ofimagery generally requires some human involvement. This is impracticalfor many applications.

Let us consider the basic principle of cost/meter as a useful metric,and imagine that various applications for exploiting satellite data arewilling to pay different amounts in order to achieve given levels ofgeocoding accuracy. The following disclosure hypothesizes that there areways (possibly novel, alluding to the idea that the author lacksdetailed knowledge of the state of the art, and presumes no novelty norlack thereof) to utilize all collected satellite data, properlyidentified and stored as a huge intercorrelated reference system—itselfanchored by ground truth data—as a means to automatically geocodeincoming raw pixels to the massive overall data set. The accuracy ofthis automated geocoding would hopefully be higher than that obtainablefrom ephemeris-type systems alone, but would probably be less accuratethan “manually instigated” precision geocoding based directly on groundtruth. The hope and goal would be that a lower core cost/meter geocodingaccuracy could be achieved.

Such a system may involve the following elemental components:

-   1) An ideal sphere with an arbitrary time origin (as the starting    point for the DEM model)-   2) A time-evolving DEM-   3) A time-evolving master-correlate albedo texture map    -   3A) A finite layered index map, organizing current raw data        contributors to map-   4) Ground Truth Data-   5) Nominal ephemeris data per contiguous datastream

The ongoing automation process includes:

-   1) Creating initial sphere, DEM, and texture map using existing    ground truth-   2) Creating a layered index map-   3) Each newly acquired datastream is cloud-masked,    DEM-projection-and refraction-corrected-   4) The masked-corrected data—using nominal ephemeris data as a    starting point—is correlated to a master DEM/albedo map, itself    projected along nominal ephemeris-   5) The quality of the new data is evaluated, and incrementally added    to the master albedo map and index map if it is deemed acceptable    -   5A) a pseudo infinite impulse response (based on time and        quality of data) in coming up with current albedo map pixel        value (omnidirectional pixel value)

At the core of building the albedo-map (and also the DEM) is the need toalways track its inputs for several reasons:

-   -   redundant checking for accuracy and veracity of inputs;    -   indexing of what data is contributing to the master albedo map;    -   coordination of data from similar or even vastly different        sources, all contributing to either the master maps or to        existing relational databases.        As detailed below, watermarking can play an important role in        the achieving these objects.

The foregoing will be clearer from the following.

Consider an illustrative DEM system with a 10 meter horizontalresolution, and featuring continual refresh and georeferencing. At twobytes per pixel, and a model size of 4M by 2M pixels, the modelcomprises 16 Terabytes of data. The albedo map is on the same order ofresolution, with the same data storage requirements. The databasestoring this information desirably is arranged to easily graph necessarycorrelation scenes.

Presume an existing master DEM and albedo map. These may have beenformed by a dozen or more redundant component data sets (e.g., aerialimages, ground surveys), acquired over the previous days, months oryears, that have been composited together to yield the final DEM/map(“model”).

Now imagine a new satellite image is acquired corresponding to part ofthe region represented by the master model. The particular terraindepicted by the satellite image can be inferred from ephemeris and otherfactors, as noted above. By such techniques, the location of thedepicted image on the earth's surface (e.g., the latitude and longitudeof a point at the center of the image) may be determined within an errorof, say 5-500 meters. This is a gross geo-referencing operation.

Next a fine geo-referencing operation is automatically performed, asfollows. An excerpt of the master model is retrieved from thedatabase—large enough to encompass the new image and its possibleplacement error (e.g., an area centered on the same latitude/longitude,but extending 250 meters further at each edge). A projective image isformed from this master DEM/map excerpt, considering, e.g., thesatellite's position and atmospheric effects, thereby simulating how themaster model would look to the satellite, taking into account—wherepossible—the particular data represented by the satellite image, e.g.,the frequency bands imaged, etc. (The albedo map may be back-projectedon the 3D DEM data in some arrangements to augment the realism of theprojective image.)

The projective image formed from the master DEM/map excerpt differssomewhat from the image actually acquired by the satellite. Thisdifference is due, in part, to the error in the gross geo-referencing.(Other differences may arise, e.g., by physical changes in the regiondepicted since the master DEM/map was compiled.)

The projective image is next automatically correlated with the satelliteimage. A variety of known mathematical techniques can be utilized inthis operation, including dot product computation, transforming tospatial frequency domain, convolution, etc. In a lay sense, thecorrelation can be imagined as sliding one map over the other until thebest registration between the two images is obtained.

From the correlation operation, the center-to-center offset between theexcerpt of the master DEM/map, and the satellite image, is determined.The satellite image can thereby be accurately placed in the context ofthe master model. Depending on system parameters, a fine placementaccuracy of, e.g., between 5 cm and 5 meters (i.e., sub-pixel accuracy)may be achieved.

(In some embodiments, affine transformations can be applied to thesatellite data to further enhance the correlation. E.g., particulargeological or other features in the two data sets can be identified, andthe satellite data (e.g., map or image) can then be affine-transformedso that these features correctly register.)

With the satellite image thus finely geo-referenced to the masterDEM/map, it can be transformed (e.g., resampled) as necessary tocorrespond to the (typically rectilinear) reference system used in themaster model, and then used to refine the data represented in the model.Buildings or other features newly depicted in the satellite image, forexample, can be newly represented in the master model. The master modelcan be similarly updated to account for erosion and other topologicalchanges revealed by the new satellite image.

Part of the finely geo-referenced satellite data may be discarded andnot added to the master model, e.g., due to cloud cover or otherobscuring phenomena. The remaining data is assessed for its relativequality, and this assessment is used in determining the relative weightthat will be given the new satellite data in updating the master model.

In one embodiment, the finely geo-referenced satellite data is segmentedinto regions, e.g., rectangular patches corresponding to terrain 1000meters on a side, and each patch is given its own weighting factor, etc.In a system with 10 meter resolution (i.e., a pixel size of 10 m², thepatch thus comprises an array of 100×100 pixels. (In some embodiments,the fine geo-referencing is done following the segmentation of theimage, with each patch separately correlated with a corresponding areain the master model.) Each patch may take the form of a separate datafile.

When the new satellite data is added to update the master model, olddata may be discarded so that it no longer influences the model.Consider an area that is imaged monthly by a satellite. Several months'worth of image data may be composited to yield the master model (e.g.,so cloud cover that obscured a region in the latest fly-over does notleave part of the model undefined). As each component image data getsolder, it may be given less and less weight, until it no longer formsany part of the master model. (Other component data, in contrast, may beretained for much longer periods of time. Map information collected byground surveys or other forms of “ground truth” information may fallinto this category.)

The master model may be physically maintained in different ways. In oneexemplary arrangement, a database stores the ten sets of data (e.g.,acquired from different sources, or at different times) for each1000×1000 meter patch. When interrogated to produce a map or other data,the database recalls the 10 data sets for each patch, and combines themon the fly according to associated weighting factors and other criteria(e.g., viewing angle) to yield a net representation for that patch. Thiscomposite patch is then combined (e.g., graphically stitched) with otheradjoining, similarly-formed composite patches, to yield a data setrepresenting the desired area.

In another embodiment, the component sets of image data are notseparately maintained. Rather, each new set of image data is used toupdate a stored model. If the new image data is of high quality (e.g.,good atmospheric seeing conditions, and acquired with a high resolutionimaging device), then the new data may be combined with the existingmodel with a 20/80 weighting (i.e., the existing model is given a weightfour-times that of the new data). If the new image data is of lowquality, it may be combined with the existing model with a 5/95weighting. The revised model is then stored, and the new data needn'tthereafter be tracked.

(The foregoing examples are gross simplifications, but serve toillustrate a range of approaches.)

The former arrangement—with the component data stored—is preferred formany applications, since the database can be queried to yield differentinformation. For example, the database can be queried to generate asynthesized image of terrain as it would look at a particular time ofday, imaged in a specified IR frequency band, from a specified vantagepoint.

It will be recognized that a key requirement—especially of the formerarrangement—is a sophisticated data management system. For each data setrepresenting a component 1000×1000 meter patch stored in the database, alarge quantity of ancillary data (meta data) must be tracked. Among thismeta data may be a weighting factor (e.g., based on seeing conditionsand sensor attributes), an acquisition date and time (from which anage-based weighting factor may be determined), the ID of thesensor/satellite that acquired that data, ephemeris data from the timeof acquisition, the frequency band imaged, the geo-referenced positionof the patch (e.g., latitude/longitude), etc., etc. (Much of this datamay be common to all patches from a single image.)

Classically, each component source of data to the system (here referredto as an “image” for expository convenience) is associated with a uniqueidentifier. Tapes and data files, for example, may have headers in whichthis identifier is stored. The header may also include all of the metadata that is to be associated with that file. Or the identifier canidentify a particular database record at which the corresponding metadata is stored. Or hybrid approaches can be used (e.g., the header caninclude a file identifier that identifies a data base record, but alsoincludes data specifying the date/time of data acquisition).

In the final analysis, any form of very reliable image identificationmay suffice for use in such a system. The header approach just-discussedis straightforward. Preferable, however, is to embed one or moreidentifiers directly into the image data itself (i.e., “in band”steganographic encoding using digital watermarking). A well-designedwatermarking name-space can in fact become a supra-structure overseveral essentially independent serial numbering systems already in useacross a range of satellite sources. Moreover, rudimentarygeoreferencing information can actually be embedded within the watermarkname-space.

For example, on initial acquisition, an initial watermark can be appliedto satellite imagery detailing the ephemeris based gross georeferencing.Once the image has been finely georeferenced, the existing watermark caneither be overlaid or overwritten with a new watermark containing thegeoreferencing information (e.g., “center lat: N34.4324352, long:W87.2883134; rot from N/S: 3.232; x2.343, y2.340, dx0.123, dy493,etc.”). These numbers essentially encode georeferencing info includingprojective and atmospheric distortions, such that when this image isDEM-projection corrected, high accuracy should be achieved.

Another way to explain the need for watermarking might be the following:Pity the first grade teacher who has a class of young upstarts whodemand a lengthy dissertation on why they should simply put their nameson their papers. The uses defy even common sense arguments, and it is nodifferent with watermarks . . . sear in a serial number and just keeptrack of it.

The assignee's U.S. Pat. No. 6,122,403, and pending application Ser. No.09/503,881, detail suitable digital watermarking techniques in whichvalues of pixels, e.g., in a 100×100 pixel patch, can be slightlyaltered so as to convey a plural-bit payload, without impairing use ofthe pixel data for its intended purpose. The payload may be on the orderof 50-250 bits, depending on the particular form of encoding (e.g.,convolution, turbo, or BCH coding can be employed to provide someerror-correcting capability), and the number of bits per pixel. Largerpayloads can be conveyed through larger image patches. (Larger payloadscan also be conveyed by encoding the information is a less robustfashion, or by making the encoding more relatively visible.)

The watermark payload can convey an image identifier, and may conveyother meta data as well. In some systems, the component image files aretagged both by digital watermark identifiers and also by conventionalout-of-band techniques, such as header data, thereby affording dataredundancy.

Watermarking may be performed in stages, at different times. Forexample, an identifier can be watermarked into an image relatively earlyin the process, and other information (such as finely geo-referencedlatitude/longitude) can be watermarked later. A single watermark can beused, with different payload bits written at different times. (Inwatermark systems employing pseudo-random data or noise (PN), e.g., torandomize some aspect of the payload's encoding, the same PN data can beused at both times, with different payload bits encoded at the differenttimes.)

Alternatively, different watermarks can be applied to convey differentdata. The watermarks can be of the same general type (e.g., PN based,but using different PN data). Or different forms of watermark can beused (e.g., one that encodes by adding an overlay signal to arepresentation of the image in the pixel domain, another that encodes byslightly altering DCT coefficients corresponding to the image in aspatial frequency domain, and another that encodes by slightly alteringwavelet coefficients corresponding to the image).

In some multiple-watermarking approaches, a first watermark is appliedbefore the satellite image is segmented into patches. A later watermarkcan be applied after segmentation. (The former watermark is typicallydesigned so as to be detectable from even small excerpts of the originalimage.)

A watermark can be applied by the imaging instrument. In someembodiments, the image is acquired through an LCD optical shutter, orother programmable optical device, that imparts an inconspicuouspatterning to the image as it is captured. (One particular opticaltechnique for watermark encoding is detailed in U.S. Pat. No.5,930,369.) Or the watermarking can be effected by systems in thesatellite that process the acquired data prior to transmission to aground station. In some systems, the image data is compressed fortransmission—discarding information that is not important. Thecompression algorithm can discard information in a manner calculated sothat the remaining data is thereby encoded with a watermark.

The ground station receiving the satellite transmission can likewiseapply a watermark to the image data. So can each subsequent systemthrough which the data passes.

As indicated, the watermark(s) can identify the imaging system, thedate/time of data acquisition, satellite ephemeris data, the identity ofintervening systems through which the data passed, etc. One or morewatermarks can stamp the image with unique identifiers used insubsequent management of the image data, or in management of meta dataassociated with the image.

A watermark can also serve a function akin to a hyperlink, e.g., asdetailed in application Ser. No. 09/571,422. For example, a userterminal can permit an operator to right-click on a region of interestin a displayed image. In response, the system can respond with a menu ofoptions—one of which is Link Through Watermark(s). If the user selectsthis option, a watermark detection function is invoked that decodes awatermark payload from the displayed image (or from a portion of theimage in which the operator clicked). Using data from the decodedwatermark payload, the terminal interrogates a database for acorresponding record. That record can return to the terminal certainstored information relating to the displayed image. For example, thedatabase can present on the terminal screen a listing of hyperlinksleading to other images depicting the same area. By clicking on such alink, the corresponding image is displayed. Or the database can present,on the user terminal screen, the meta-data associated with the image.

In some embodiments, watermarks in component images may carry-throughinto the master DEM/map representation. If an excerpt of the masterDEM/map is displayed, the user may invoke the Link Through Watermark(s)function. Corresponding options may be presented. For example, the usermay be given the option of viewing each of the component images/datasets that contributed to the portion of the master model being viewed.

(It will be recognized that a variety of user interface techniques otherthan right-clicking, and selecting from a menu of options therebydisplayed, can be employed. That interface is illustrative only.)

In some embodiments, a watermark can be applied to each DEM/map from themaster database as it is retrieved and output to the user. The watermarkcan indicate (i.e., by direct encoding, or by pointing to a databaserecord) certain data related to the compiled data set, such as thedate/time of creation, the ID of the person who queried the database,the component datasets used in preparing the output data, the databaseused in compiling the output data, etc. Thereafter, if this output datais printed, or stored for later use, the watermark persists, permittingthis information to be later ascertained.

Watermarks can be applied to any data set (e.g., a satellite image, or amap generated from the master database) for forensic tracking purposes.This is particularly useful where several copies of the same data setare distributed through different channels (e.g., provided to differentusers). Each can be “serialized” with a different identifier, and arecord can be kept of which numbered data set was provided to whichdistribution channel. Thereafter, if one of the data sets appears in anunexpected context, it can be tracked back to the distribution channelfrom which it originated.

Some watermarks used in the foregoing embodiments can be “fragile.” Thatis, they can be designed to be lost, or to degrade predictably, when thedata set into which it is embedded is processed in some manner. Thus,for example, a fragile watermark may be designed so that if an image isJPEG compressed and then decompressed, the watermark is lost. Or if theimage is printed, and subsequently scanned back into digital form, thewatermark is corrupted in a foreseeable way. (Fragile watermarktechnology is disclosed, e.g., in applications Ser. Nos. 09/234,780,09/433,104, 09/498,223, 60/198,138, 09/562,516, 09/567,405, 09/625,577,09/645,779, and 60/232,163.) By such arrangements it is possible toinfer how a data set has been processed by the attributes of a fragilewatermark embedded in the original data set.

Assuming that early testing proves out that the addition of“watermarking energy” into the normal workflow of satellite imagingsystems does not materially disturb the function of most of the outputof that system, nevertheless certain “watermark removal” tools can bebuilt to alleviate any problems in cases where unacceptable impact isidentified. This can either be a generic tool or one highly specializedto the particular application at hand (perhaps employing secret dataassociated with that application). In a second generation system(without too much fanfare) a fairly simple “remove watermark beforeanalyzing this scene” function could be automatically included withinanalysis software such that 99% of image analysts wouldn't know or careabout the watermarking on/off/on/off functionality as a function ofuse/transport.

As will be apparent, the technology detailed herein may be employed inreconnaissance and remote sensing systems, as well as in applicationssuch as guidance of piloted or remotely piloted vehicles.

To provide a comprehensive disclosure without unduly lengthening thisspecification, applicant incorporates by reference, in their entireties,the disclosures of the above-cited patents and applications.

It should be understood that the technology detailed herein can beapplied in the applications detailed in the cited DEM patents, as wellas in other mapping and image (or audio or video or other content) assetmanagement contexts. (Likewise, the technologies detailed in the citedpatents can be advantageously used in embodiments according to thepresent invention.)

While particular reference was made to Digital Elevation Models andalbedo maps, the same principles are likewise applicable to other formsof maps, e.g., vegetative, population, thermal, etc., etc.

While the illustrated embodiment correlated the incoming imagery with aprojective image based on the master DEM/map, in other embodiments areference other than the master DEM/map may be used. For example, aprojection based just on part of the historical data from which theDEM/map was compiled can be used (e.g., one or more component data setsthat are regarded as having the highest accuracy, such as based directlyon ground truths).

Although not belabored, artisans will understand that the systemsdescribed above can be implemented using a variety of hardware andsoftware systems. One embodiment employs a computer or workstation witha large disk library, and capable database software (such as isavailable from Microsoft, Oracle, etc.). The registration, watermarking,and other operations can be performed in accordance with softwareinstructions stored in the disk library or on other storage media, andexecuted by a processor in the computer as needed. (Alternatively,dedicated hardware, or programmable logic circuits, can be employed forsuch operations.)

Certain of the techniques detailed above find far application beyond thecontext in which they are illustrated. For example, equipping an imaginginstrument with an optical shutter that impart a watermark to an imagefinds application in digital cinema (e.g., in watermarking a theatricalmovie with information indicating the theatre, date, time, andauditorium of screening).

In view of the wide variety of embodiments to which the principles andfeatures discussed above can be applied, it should be apparent that thedetailed embodiments are illustrative only and should not be taken aslimiting the scope of the invention. Rather, I claim as my invention allsuch modifications as may come within the scope and spirit of thefollowing claims and equivalents thereof. (For expository convenience,the term “map” as used in the claim should be construed to encompassterrain models, such as DEMs.)

1. A method comprising: capturing video depicting at least a portion ofthe earth's surface, the video captured by an aerial, unmannedapparatus; compressing the captured video; obtaining geographicalmetadata associated with at least the captured video; and hiding a firstdigital watermark in the compressed captured video through alterationsto data representing the compressed video, wherein the first digitalwatermark is generally imperceptible to a human observer of the video,and wherein the first digital watermark comprises a plural-bit payloadincluding or linking to at least some of the geographical metadataassociated with the captured video.
 2. The method of claim 1 furthercomprising wirelessly communicating the compressed, watermarked capturedvideo.
 3. The method of claim 1 wherein the geographical metadatacomprises at least a camera viewing angle.
 4. The method of claim 1wherein the geographical metadata comprises at least camera sensorattributes.
 5. The method of claim 1 wherein the geographical metadatacomprises at least an acquisition date and time.
 6. The method of claim1 wherein the geographical metadata comprises at least an identifierassociated with the aerial, unmanned apparatus.
 7. The method of claim 1wherein the geographical metadata comprises at least a geo-referencedposition.
 8. The method of claim 7 wherein the geo-reference position isconveyed in terms of at least latitude and longitude.
 9. The method ofclaim 7 wherein the geo-referenced position corresponds to at least someof the portion of the earth's surface depicted in the video.
 10. Themethod of claim 1 further comprising inserting a second digitalwatermark into the video, the second digital watermark comprising aplural-bit payload that includes data representing a refinement to thegeographical metadata.
 11. The method of claim 1 wherein thegeographical metadata comprises a first geolocation and a secondgeolocation, wherein the first geolocation and the second geolocationrespectively correspond to first and second locations depicted in thevideo.
 12. A machine-readable medium comprising executable instructionsstored thereon, said instructions comprising instructions to: receivevideo depicting at least a portion of the earth's surface, the videocaptured by an aerial, unmanned apparatus; compress the received video;receive geographical metadata associated with the received video; hide afirst digital watermark in the compressed received video by introducingalterations to data representing the compressed video, wherein the firstdigital watermark is hidden to be generally imperceptible to a humanobserver of the video; and wherein the digital watermark comprises aplural-bit payload including or linking to at least some of thegeographical metadata associated with the captured video.
 13. Themachine-readable medium of claim 12 further comprising instructions tohide a second digital watermark in the received, compressed video, thesecond digital watermark comprising a plural-bit payload that includesdata representing a refinement to the at least some geographicalmetadata.
 14. The machine-readable medium of claim 12 wherein thegeographical metadata comprises a first geolocation and a secondgeolocation, wherein the first geolocation and the second geolocationrespectively correspond to first and second locations depicted in thevideo.
 15. The machine-readable medium of claim 12 wherein thegeographical metadata comprises at least a geo-referenced position. 16.The machine-readable medium of claim 15 wherein the geo-referenceposition is conveyed in terms of at least latitude and longitude. 17.The machine-readable medium of claim 15 wherein the geo-referencedposition corresponds to at least some of the portion of the earth'ssurface depicted in the video.
 18. The machine-readable medium of claim12 wherein the medium comprises electronic memory storage.
 19. A methodcomprising: capturing video depicting at least a portion of the earth'ssurface, the video captured by an aerial, unmanned apparatus;compressing the captured video; hiding first digital watermarking in thecompressed captured video through alterations to data representing thecompressed video, wherein the first digital watermarking is generallyimperceptible to a human observer of the video, and wherein the firstdigital watermarking comprises at least a first plural-bit payloadincluding or linking to at least first geographical metadata associatedwith the captured video; hiding second digital watermarking in thecompressed captured video through alterations to data representing thecompressed video, wherein the second digital watermarking is generallyimperceptible to a human observer of the video, and wherein the seconddigital watermarking comprises at least a second plural-bit payloadincluding or linking to at least second, different geographical metadataassociated with the captured video.
 20. The method of claim 19 whereinat least the first geographical metadata or the second, differentgeographical metadata comprises at least one item of metadata from agroup comprising: camera viewing angle; camera sensor attributes; anacquisition date and time; an identifier associated with the aerial,unmanned apparatus; and a geo-referenced position.
 21. The method ofclaim 19 wherein the first geographical metadata comprises a firstgeo-reference position conveyed in terms of at least latitude andlongitude and the second, different geographical metadata comprises asecond geo-reference position conveyed in terms of at least latitude andlongitude.
 22. The method of claim 21 wherein the first geo-referencedposition corresponds to at least a first portion of the earth's surfacedepicted in the video and the second geo-referenced position correspondsto at least a second, different portion of the earth's surface depictedin the video.
 23. A machine-readable medium comprising instructionsstored thereon to carry out the method of claim
 19. 24. The method ofclaim 1 wherein the aerial, unmanned apparatus comprises an unmannedaircraft.
 25. The method of claim 24 wherein the unmanned aircraftcomprises a remotely piloted aircraft.
 26. The method of claim 1 furthercomprising: hiding a second digital watermark in the compressed capturedvideo through alterations to data representing the compressed video,wherein the second digital watermark is generally imperceptible to ahuman observer of the video, and wherein the second digital watermarkcomprises a plural-bit payload including or linking to at least some ofthe geographical metadata associated with the captured video.
 27. Themethod of claim 26 wherein the first digital watermark correlates atleast some of the geographical metadata to a first portion of the video,and the second digital watermark correlates as least some of thegeographical metadata to a second, different portion of the video. 28.The method of claim 27 wherein the first portion corresponds to a firstgeolocation and the second portion corresponds to a second, differentgeolocation.
 29. The method of claim 19 wherein the aerial, unmannedapparatus comprises an unmanned aircraft.
 30. The method of claim 29wherein the unmanned aircraft comprises a remotely piloted aircraft. 31.The method of claim 19 wherein the aerial, unmanned apparatus comprisesa satellite.
 32. A method comprising: capturing video depicting at leasta portion of the earth's surface, the video captured by an aerial,unmanned apparatus; hiding first digital watermarking in captured videothrough alterations to data representing the captured video, wherein thefirst digital watermarking is generally imperceptible to a humanobserver of the captured video, and wherein the first digitalwatermarking comprises at least a first plural-bit payload comprising orindexing at least first geographical metadata associated with thecaptured video; hiding second digital watermarking in the captured videothrough alterations to data representing the captured video, wherein thesecond digital watermarking is generally imperceptible to a humanobserver of the captured video, and wherein the second digitalwatermarking comprises at least a second plural-bit payload comprisingor indexing at least second, different geographical metadata associatedwith the captured video.
 33. The method of claim 32 wherein the firstgeographical metadata corresponds to a first geolocation depicted in thecaptured video and the second, different geographical metadatacorresponds to a second, different geolocation depicted in the capturedvideo.
 34. The method of claim 32 wherein the aerial, unmanned apparatuscomprises an unmanned aircraft.
 35. The method of claim 34 wherein theunmanned aircraft comprises a remotely piloted aircraft.
 36. The methodof claim 32 wherein the aerial, unmanned apparatus comprises asatellite.
 37. The method of claim 32 wherein the data representing thecaptured video comprises DCT coefficients.
 38. The method of claim 32wherein the data representing the captured video comprises a compressedform.
 39. The method of claim 32 wherein the first digital watermarkingcorrelates the first geographical metadata to a first portion of thecaptured video and the second digital watermarking correlates thesecond, different geographical metadata to a second, different portionof the captured video.
 40. The method of claim 1 wherein the aerial,unmanned apparatus comprises a satellite.